Micro/macro damage evaluation of flat braided composites with a circular hole

In this study, attention is paid to braided fabrics as the form of reinforc ing fiber in composite materials and the influence of a circular hole on th e mechanical properties of a flat braided composite is investigated. Two ty pes of specimens are prepared; a flat braided bar with a braided hole in wh ich the fiber bundle is continuous around the hole, and one with a machined hole. The effects of a circular hole on fracture behavior in the braided f lat bar is examined by static tensile and fatigue testing. Moreover, specim ens with a pin inserted at the circular hole are also examined under static tensile loading. In order to evaluate damage, macro and micro damage obser vations are carried out. From the results of static tensile and fatigue testing, the flat bar with a braided hole had higher performance than the flat braided bar with the mac hined hole. Furthermore, difference of damage propagation and dominant fact or of fracture in the two types of flat braided composites with a circular hole was confirmed by macro and micro observation. Damage at the composite with a hole by machining work depends on the interface between fiber bundle s and was confirmed to concentrate around a hole. Beside, damage at the com posite with a hole by application of braiding technique depends on continuo usly oriented fiber in the longitudinal direction. Consequently, it is cons idered that a performance of the reinforcing fiber properly works in the ca se that reinforcement configuration is braided fabric.